Dental casting alloy



45 torch; When fully molten the alloy is centrifu- In my alloy composition I prefer to limit any 4,5

Patented July 11,1939 Q g 2,165,849

UNITED STATES PATENT OFFICE Cornell Joel Grossman, Millburn, N. J.

No Drawing. Application May 23, 1939,

Serial No. 275,231 a 2 Claims. .(01. 75-171) This invention relates to metallurgy and more used during the melting operation of chromium particularly to an alloy suitable for use in the containing alloys, excessive oxidation of the metal manufacture of cast dentures and the like. constituents occurred and voids caused by oxide In the manufacture of metallic dentures the and gas occlusions are obtained. This circumt alloy composition employed must be stainless and stance has greatly limited the use and adapta- 5 non-corrosive towards various acid and alkaline tion of chromium-containing alloys, particularly reagents present in the mouth or-various foods in the forming of cast dentures, due to the fact and liquids. The alloy also must be wea'r-resistthat when molten or during melting the chroant and the alloy must be variable as to permium contents of such an alloy or. alloys rapidly in centages' of the. several constituents to a suflioxidize to form diflicultly fusible oxi e comm cient extent and .flexibility. permitting its use pounds even though the alloy haslbeem covered under a wide variety of service conditions. or protected by readily fusible slag materials. Moreover, the alloy composition must be adapted I have found-that the most ef ective Way t to be readily cast free from blow-holes and prevent the oxidation of the chromium in chrowith a minimum of material surplus, by the ordimiumcontaining alloys is to incorporate in the 1 nary methods practised in the art. alloy the alloy-constituent which is more readily The present invention aims to provide an alloy oxidizable than the chromium and which on oxiadapted to meet these manyv conditions and furdation forms a relatively low melting-slag operther aims to provide a denture comprised of the ating to protect the alloy from direct contact said alloy. The alloy composition of the present with oxidizing agents. Boron is the only alloy 20 invention comprises a base consisting of cobalt constituent of which I am aware that will acand chromium in such relative proportions of complish this desired result. 'The amountof the cobalt to give the required strength, toughboron I may'incorporate in the alloy composiness and where resistant properties are desired, tion of the present invention may vary widely and chromium in sufiicient amountto render the -without departure. I' have successfully employed 2! base stainless and corrosion-resistant. Into this as low as 1.00% and as high as 10%. Under base I may incorporate manganese or silicon or very expert manipulating conditions of melting both in such amounts as willbe necessary to and casting a boron content of less than 1.0% completely deoxidize the alloy and to completely probably can be employed but under the ordinary 3n neutralize, the deleterious eifect of any sulphur manipulating'conditions of melting and casting or carbon present in the base and I. may also I prefer to have present in my alloy about 5.0% incorporate a percentage of molybdenum or boron, as this amount permits of repeated retungsten or both in such an amount as will melting without detrimental results to the alloy. augment the normal strength and rigidity of The excess boron does not appearto be delethe base. Into the base or base improved by terious in the alloy but to .the contrai'y appears 8 additions of one or. more of. the metals manto increase the fluidity of the alloy when molten ganese, molybdenum and tungsten, I incorporate and the ease with which it may be cast, and a sufficient percentage of boron as will effectively cast dentures of my alloy containing 5.0% or protect the alloy constituents from oxidation more of boron appear to be more sharply defined 40 during the subsequent re-melting and casting to than those containing 1 to 2% boron. This 0 form dentures. Inthe manufacture of dentures amount of boron, moreover, appears to benefiit is customary in the art to melt the alloy in cially affect the physical properties of the alloy, an open crucible by impinging thereon the open making it of finer grain structure and improving flame of an oxyacetylene or oxy-hydrogen blow its hardness and luster.

gally cast into a mold wherein relatively rapid iron content to less than 1.00%. Iron in amounts solidification occurs. Heretofore 'in the art it greater than this, while being of advantage in has been diflicult, to manufacture cast dentures some respects, such as giving added strength and of metals in this manner due to the fact that ductility, detrimentally affect the corrosion re- 5 it is impractical to employ a protective slag over sistance properties and require added chromium the metal du e melting and Casting Opflttto counteract the same. For this reason I prefer tlons, as the slag, when used, also entered .the to limit my invention to a cobalt chromium base mold and w s n r pp by the p y f olldiwith iron less than 1 0%. In this base alloy the Wing metal, causing blow-holes, voids and the chromium content may vary from 5% to 45% and like. When. ho e a Protective -8 was not the cobalt content may vary from 45% .to 9.4% u

with the remainder of the alloy consisting of boron up to 10% but preferably about 5% and manganese 1 to 2%, or silicon up to one (1%) or both. I find it preferable to increase the cobalt with decreasein chromium within the ranges specified although this relation is not empirical but solely for the purpose of maintaining relatively constant corrosion resistance properties in the alloy. where molybdenum or tungsten or both are added to the alloy as stiffening constituents. I prefer to add these elements as replacements for part of the cobalt and in this respect the cobalt, molybdenum and tungsten are to be considered to be substantial equivalents, although each in addition contribute to the corrosion resistant properties of the alloy. The molybdenum content may be as high as 8% but preferably should be in the range 2 to 4%. content may be as high as 4%, but preferably zo should be in range of l to 2%.

As an example of the present invention, alloys that I have found most suitable for general purpose used in the casting of dentures have the following analyses:

I II III Percent Percent Percent Chromium 25. 0 30. O0 15. 00 Cobalt 69. 0 62. 00 77. 00

0 1.0 max 1.0 max.

1. 0 l. 0 l. 0 5.0 5. 0 5. 0 0 1.0 1.0 max.

Alloys suitable for the same purpose but stronger and more suitable forbridge-work are similar to composition No. l, but contain molybdenum 2-8% with the cobalt reduced a corresponding amount or tungsten 1-4% with the cobalt reduced to a corresponding amount.

Where a softer alloy is desired, as in forming of pins, bars and the like, which subsequently are to be bent in shape, I increase the cobalt content to about 90% and lower the chromium -contents to less than 10% with about 1% of The tungstenof the present invention I sometime prefer a chromium titanium alloy instead of chromium as an ingredient and a manganese boron alloy. These alloys should be preferably substantially free from carbon and from iron. I then mix the chromium, titanium and manganese boron alloys together with cobalt, preferably in smallsized pieces, in such relative amounts as will give me the alloy composition desired, and melt the same down in the electric induction furnace under conditions protecting the metal from oxidation. When fully molten the alloy is cast in the mold adapted to form relatively small diameter rods which after solidification may be cut or broken into relatively small pieces.

In the forming of dentures of this alloy, a. suflicient amount of these small-sized pieces of rod is placed in an open crucible and is melted by the direct application thereon of the oxyacetylene or oxy-hydrogen flame and as soon as the metal becomes molten and fluid the molten metal is cast centrifugally into the denture mold as heretofore practised in the art. The thus formed cast denture will be substantially free from blow-holes, voids and oxide and slag inclusions. Any boron which is oxidized during the melting prior to casting, forms such a fluid slag that on entering the mold during casting the same does not interfere with the entrance of the molten metal into the finest crevices of the mold, and a clearly defined sound casting will be obtained. I

Boron may be increased without deleterious effect. Skilled technicians may employ an alloy with less boron.

From the above description of the present invention, it will be apparent that the same may be widely varied as to alloy composition without departure from the invention and all such modifications and variations are contemplated as may fall within the scope of the following claims.

What I claim is:

1. A casting alloy for dentures and the like, comprising 3-45% chromium; 1-10% boron; .2-2% silicon; .2'5% manganese, balance cobalt.

2. A casting alloy for sound denture castings and the like, containing .5-l0% boron; boron being in at least suflicient amount so that upon re-melting and casting a sound non-oxidized casting is obtained; chromium 31-45%; silicon .22%; manganese .2-5%; balance cobalt.

CORNELL JOEL GROSSMAN. 

